Welcome Perrysr to the HDTimeline forum. I have to say your symptom caught me by surprise...I would have expected your headlight to get brighter when giving gas. I suspect that you have a bad connection as an increase in RPMs would only spin up the stator/charging system to produce more power (if it does not drop before increasing) UNLESS there is a bad ground, battery connections, interconnect plugs, or fuses in the block. I would get a good contact cleaner from an electronics store retailer like Radio Shack, scrape and wash all connections, and coat with dielectric grease. I would check where any mods were done under the seat, side covers and handlebar control areas. Could be a pinched wire...or even a loose connection or ground in the headlight shell if that is the ONLY symptom of a problem. Engine RPM should be high enough at idle and battery charge great enough not to dim at all.